feat(sway): add the nemo file manager (themed, Mod+e)

Install nemo and bind it to Mod+e (mkForce, overriding the module
default `layout toggle split`). Add a home-manager `gtk` block so GTK
apps match the desktop: the Catppuccin Mocha GTK theme
(catppuccin-gtk, mocha/blue), with Adwaita icons + cursor as before.
Under Sway GTK reads ~/.config/gtk-*/settings.ini directly (no XSettings
daemon), so this themes nemo without extra env.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lyrathorpe/home/desktop.nix

@@ -11,6 +11,7 @@
   home.packages = [
     pkgs.element-desktop
     pkgs.legcord
+    pkgs.nemo # file manager (launched via Mod+e, see ./sway.nix)
     #pkgs.plex-desktop
     #pkgs.plexamp
   ];
@@ -20,6 +21,25 @@
     XDG_CURRENT_DESKTOP = "sway";
   };
 
+  # Theme GTK apps (nemo, etc.) to match the Catppuccin Mocha desktop. Under
+  # Sway there is no XSettings daemon, so GTK reads these from the generated
+  # ~/.config/gtk-{3,4}.0/settings.ini directly. The Mocha theme is dark by
+  # design, so no separate prefer-dark hint is needed.
+  gtk = {
+    enable = true;
+    theme = {
+      name = "catppuccin-mocha-blue-standard";
+      package = pkgs.catppuccin-gtk.override {
+        accents = [ "blue" ];
+        variant = "mocha";
+      };
+    };
+    iconTheme = {
+      name = "Adwaita";
+      package = pkgs.adwaita-icon-theme;
+    };
+  };
+
   home.pointerCursor = {
     gtk.enable = true;
     x11 = {

lyrathorpe/home/sway.nix

@@ -131,6 +131,8 @@ in
           # Mod+Space (focus mode_toggle); a plain value would conflict with it
           # at equal priority. Mod+d also still runs the launcher (module default).
           "${modifier}+space" = lib.mkForce "exec ${menu}";
+          # File manager. mkForce overrides the module default (layout toggle split).
+          "${modifier}+e" = lib.mkForce "exec ${pkgs.nemo}/bin/nemo";
           "${modifier}+l" = "exec ${pkgs.swaylock}/bin/swaylock -f";
           "Print" = "exec ${pkgs.grim}/bin/grim ~/screenshot-$(date +%F-%H%M%S).png";
           "XF86AudioRaiseVolume" = "exec ${pkgs.wireplumber}/bin/wpctl set-volume @DEFAULT_AUDIO_SINK@ 5%+";